This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to Japanese Patent Application No. 193574/1999 filed in Japan on Jul. 7, 1999 and Japanese Patent Application No. 293003/1999 filed in Japan on Oct. 14, 1999; the entire content of which is hereby incorporated by reference.
1. Field of the Invention
This invention relates to crystallized glasses suitable for substrates which are used for information recording media, such as magnetic disks, optical disks and optical magnetic disks, substrates for information recording media composed of this crystallized glass, and information recording media using said substrate for information recording medium.
2. Description of the Related Art
Major components of magnetic storage devices of electronic computers and the like are a magnetic recording medium and a magnetic head for reconstruction of magnetically recorded information. Flexible disks and hard disks have been known as magnetic recording media. As substrates for hard disks, aluminum alloy has been mainly used. Recently, flying height of magnetic heads is markedly reduced as hard disk drivers for notebook personal computers are made smaller and their magnetic recording density made higher. Accordingly, extremely high precision has been demanded for the surface smoothness of magnetic disk substrates. However, it is difficult to produce smooth surface more than a certain level of precision with an aluminum alloy. That is, even though it is polished using highly precise abrasives and processing apparatuses, the polished surface may suffer from plastic deformation because of the low hardness of the alloy. Even if the aluminum alloy is plated with nickel-phosphorous, the surface roughness Ra cannot be made equal to or less than 5 xc3x85 (angstrom). In addition, as hard disk drivers are made smaller and thinner, a further smaller thickness of substrates for magnetic disks is also strongly desired. However, it is difficult to produce such a thin disk with an aluminum alloy having a certain strength defined by specification of hard disk drivers because of low strength and stiffness of aluminum alloy.
Therefore, glass substrates for magnetic disks of which high strength, high stiffness, high impact resistance and high surface smoothness are required have been developed. Among these, chemically reinforced glass substrates whose surfaces are strengthened by the ion exchange technique, crystallized glass substrates subjected to crystallization treatment and the like have been known well.
As a chemically reinforced glass substrate by ion-exchange, for example, a glass disclosed in Japanese Patent Unexamined Publication No. Hei. 1-239036 (JP-A-239036/89) has been known. This chemically reinforced glass substrate is such a glass substrate for magnetic disks as the glass containing, indicated in terms of % by weight, 50-65% of SiO2, 0.5-14% of Al2O3, 10-32% of R2O where R is an alkali metal ion, 1-15% of ZnO and 1.1-14% of B2O3 is reinforced by forming a crushing stress layer on the glass substrate with an ion exchange method by an alkali ion.
In addition, as a crystallized glass, for example, a glass disclosed in Japanese Patent Examined Publication No. 2516553 is exemplified. This crystallized glass is such a crystallized glass for magnetic disks which contains, indicated in terms of % by weight, 65-83% of SiO2, 8-13% by Li2O, 0-7% of K2O, 0.5-5.5% of MgO, 0-5% of ZnO, 0-5% of PbO (provided that MgO+ZnO+PbO is 0.5-5%), 1-4% of P2O5, 0-7% of Al2O3 and 0-2% of As2O3+Sb2O3, and contains micro crystalline particles of Li2O.2SiO2 as main crystals.
Moreover, a crystallized glass is also disclosed in Japanese Patent Unexamined Publication No. Hei. 7-291660 (JP-A-291660/95). This crystallized glass is obtained by heat treatment after fusion and forming a glass which consists of, indicated in terms of % by weight, 38-50% of SiO2, 18-30% of Al2O3, 10-20% of MgO, provided that having a composition containing, indicated in terms of weight ratio, 1.2-2.3 of Al2O3/MgO, 0%-5% of B2O3, 0%-5% of CaO, 0%-5% of BaO, 0%-5% of SrO, 0.5%-7.5% of ZnO, 4%-15% of TiO2, 0%-5% of ZrO2 and 0%-2% of As2O3 and/or Sb2O3. This glass is a cordierite based crystallized glass characterized by containing cordierite based crystals as crystals. Moreover, a substrate for magnetic disks composed of this crystallized glass is also disclosed.
In addition, a crystallized glass is also disclosed in Japanese Patent Unexamined Publication No. Hei. 9-77531 (JP-A-77531/97) (U.S. Pat. No. 5,476,821). This crystallized glass is a ceramic product having the Young""s modulus in the range of from about 14xc3x97106-about 24xc3x97106 psi (96-165 GPa) and the fracture toughness of more than 10 MPaxc2x7mxc2xd. In addition, this crystallized glass consists of crystalline phase laminated body which mainly consists of crystals having a spinel structure and a uniform size and dispersing uniformly in a siliceous-rich residual matrix. This is a glass ceramic which substantially consists of, indicated in terms of % by weight using oxides as a standard, 35-60% of SiO2, 20-35% of Al2O3, 0-25% of MgO, 0-25% of ZnO, 0-20% of TiO2, 0-10% of ZrO2, 0-2% of Li2O and 0-8% of NiO. This has at least about 10% of a total amount of MgO+ZnO and may contain equal to or less than 5% of an optional component selected from the group composed of BaO, CaO, PbO, SrO, P2O5, B2O3 and Ga2O3, in the range of from 0 to 5% of R2O selected from the group consisting of Na2O, K2O, Rb2O and Cs2O, and in the range of from 0 to 8% of transition metals. In the case of containing less than about 25% of Al2O3, this is a glass ceramic having a composition in which the total amount of TiO2+ZrO2+NiO is equal to or more than 5%. In above publication, the substrate for magnetic disks consisting of this glass ceramic is disclosed.
In addition, a crystallized glass is also disclosed in U.S. Pat. No. 5,491,116. This crystallized glass is a glass ceramic product having the fracture coefficient of at least about 15,000 psi, the Knoop hardness exceeding about 760 KHN, the Young""s modulus of more than about 20xc3x97106 psi and the fracture toughness of more than 1.0 MPaxc2x7mxc2xd. The main crystals of the crystallized glass are enstatite or its solid solution and spinel (spinel structure crystal), and the crystallized glass contains at least 92% of the composition substantially composed of, indicated in terms of % by weight, 35-60% of SiO2, 10-30% of Al2O3, 12-30% of MgO, 0-10% of ZnO, 5-20% of TiO2 and 0-8% of NiO. Moreover, the substrate for magnetic disks composed of this crystallized glass is also disclosed. It is to be noted that the same glass as the crystallized glass disclosed in aforementioned patent is also disclosed in Journal of Non-Crystalline Solids 219(1997) 219-227.
However, along with making hard disks smaller and thinner and making recording density higher, it is rapidly developed to make flight height of magnetic heads smaller and revolution speed of disks higher. Thereby, substrate materials are more strictly required the strength, the Young""s modulus, the smoothness of the surface and the like. In particular, by making the information recording density of 3.5-inch hard disks for personal computers and severs higher, the surface smoothness and the surface flatness of the substrate materials are strictly required. In addition, corresponding to the higher data processing speed, it is required to set the winding number of the disks equal to or higher than 10,000 rpm. Thus, the requirement for stiffness of substrate materials becomes increasingly severer, and the limitation of conventional aluminum substrates already becomes obvious. In future, as long as it is necessarily demanded to make the capacity of hard disks higher and to make the revolution speed of hard disks higher, it is clear that the substrate materials for magnetic recording medium is strongly required to exhibit higher Young""s modulus, higher strength, more excellent surface flatness, higher impact resistance and the like.
However, such a chemically reinforced glass as disclosed in Japanese Patent Unexamined Publication No. Hei. 1-239036 (JP-A-239036/89) mentioned above has the Young""s modulus of about 80 GPa, therefore, it cannot meet the strict demand for hard disks in future. As for conventional chemically reinforced substrate glasses, alkali ions are introduced in a large amount in the glass for ion exchange, so that the reinforced glasses mostly have the low Young""s modulus (90 GPa). Moreover, due to also having low stiffness, it cannot meet 3.5-inch high-end disk substrates and thinner disk substrates. In addition, the glass chemically reinforced by ion exchange contains large amount of alkali components. Thus, if it is used for long hours under the circumstance of high temperature and high humidity, alkali ions deposit from parts including thin magnetic films or exposing glasses, such as a pinhole part of a magnetic film or a circumference of a magnetic film. It has a disadvantage that this triggers a corrosion or decomposition of the magnetic films. In the producing process of the magnetic recording medium, after providing a magnetic layer on the glass substrate, certain heat treatment may be carried out in order to improve characteristics such as coercive force of the magnetic layer However, the conventional ion-exchanged reinforced glass mentioned above has at most 500xc2x0 C. of the glass transition temperature, so that it has poor heat resistance. Thereby, it has a problem that higher coercive force cannot be obtained.
In addition, the conventional crystallized glass as disclosed in Japanese Patent Publication No. 2516553 mentioned above is superior a little in the Young""s modulus and heat resistance than aforementioned chemically reinforced glass substrate. However, the surface roughness is equal to or higher than 10 xc3x85, thereby the surface smoothness is poor, so that it is limited to make the flying height smaller. Therefore, it has a problem that it cannot meet higher magnetic recording density. Moreover, the Young""s modulus is about from 90 to 100 GPa at most, so that it also cannot meet 3.5-inch high-end disk substrates and thinner disk substrates.
In addition, the crystallized glass disclosed in Japanese Patent Unexamined Publication No. Hei. 7-291660 (JP-A-291660/95) mentioned above has the Young""s modulus of about from 100 to 130 GPa, therefore, it cannot be said that it is sufficient. Moreover, it has only such a surface smoothness as having the Young""s modulus of about 8 xc3x85, resulting in poor smoothness. Additionally, the temperature of glass liquid phase is high which is 1400xc2x0 C., so that it has a disadvantage of difficulty in producing.
Moreover, the crystallized glass disclosed in Japanese Patent Unexamined Publication No. Hei. 9-77531 (JP-A-77531/97) mentioned above has a disadvantage of large difficulty in polishing because the main crystals are spinel.
Moreover, a large amount of enstatite is contained together with spinel in the crystallized glass disclosed in U.S. Pat. No. 5,491,116 and Journal of Non-Crystalline Solids 219(1997) 219-227. Accordingly, it can be considered that easiness in polishing is more improved than the crystallized glass disclosed in Japanese Patent Unexamined Publication No. Hei. 9-77531 (JP-A-77531/97). However, because spinel is still contained therein, it is difficult to say that it has sufficient polishing characteristics. That is, it still takes a long time for polishing required for obtaining desirable surface roughness, so that it has a problem of inferior productivity
Moreover, because a glass disclosed in Japanese Patent Publication No. 2648673 is a fire-resistant glass ceramic for the purpose of using temperature equal to or higher than 1200xc2x0 C., it is difficult to be used as a substrate for information recording medium. That is, it is difficult to be produced due to high melting temperature, moreover, the surface smoothness required for information recording medium cannot be obtained due to large crystal size.
Therefore, it is an object of the present invention to provide a substrate for information recording medium, such as magnetic disks and the like, consisting of crystallized glass which has higher Young""s modulus, higher strength and higher fire-resistance, superior in the surface smoothness, surface homogeneity and surface processability with considering demands that a substrate for magnetic recording medium will be made thinner and will have high strength, high heat resistance, high impact resistance and the like in near future, as well as it can be cheaply produced due to comparatively low temperature of the glass liquid phase.
Moreover, it is also an object of the present invention to provide information recording media using the substrate composed of aforementioned crystallized glass, such as magnetic disks.
In addition, the present invention provides a production method of the substrate for information recording medium composed of aforementioned crystallized glass.
To solve objects mentioned above, the inventors carried out various examinations, as results, it is found that crystallized glass suitable for substrate for information recording medium which has high Young""s modulus equal to or higher than 140 GPa, good surface smoothness, and comparatively low liquid temperature. Then, they accomplished the present invention.
The present invention relates to a substrate for information recording medium (hereinafter referred to substrate 1) composed of crystallized glass comprising
SiO2: 35-65 mol %
Al2O3: 5-25 mol %
MgO: 10-40 mol % and
TiO2: 5-15 mol %,
wherein the sum of the above components is equal to or more than 92 mol %, and main crystals contained in the crystallized glass are enstatite and/or its solid solution.
With the substrate above, a molar ratio of Al2O3 to MgO (Al2O3/MgO) may be from equal to or more than 0.2 to less than 0.5.
With the substrate above, the crystallized glass preferably comprises
SiO2: 40-60 mol %
Al2O3: 7-22 mol %
MgO: 12-35 mol % and
TiO2: 5.5-14 mol %.
With the above substrate 1, the crystallized glass may comprise Y2O3 in an amount equal to or less than 10 mol %.
With the above substrate 1, the crystallized glass may comprise ZrO2 in an amount equal to or less than 10 mol %.
The present invention further relates to a substrate for information recording medium (hereinafter referred to substrate 2) composed of crystallized glass consisting essentially of
SiO2: 35-65 mol %
Al2O3: 5-25 mol %
MgO: 10-40 mol %
TiO2: 5-15 mol %
Y2O3: 0-10 mol %
ZrO2: 0-10 mol %
R2: 0-5 mol % (wherein R is at least one selected from the group of Li, Na and K)
RO: 0-5 mol % (wherein R is at least one selected from the group of Ca, Sr and Ba)
As2O3+Sb2O3: 0-2 mol %
SiO2+Al2O3+MgO+TiO2: 92 mol % or more; and main crystals contained in the crystallized glass are enstatite and/or its solid solution.
The present invention further relates to a substrate for information recording medium (hereinafter referred to substrate 3) composed of crystallized glass consisting essentially of
SiO2: 35-65 mol%
Al2O3: 5-25 mol %
MgO: 10-40 mol %
TiO2: 5-15 mol %
Y2O3: 0-10 mol %
ZrO2: 0-10 mol %
R2O: 0-5 mol % (wherein R is at least one selected from the group of Li, Na and K)
RO: 0-5 mol % (wherein R is at least one selected from the group of Ca, Sr and Ba)
As2O3+Sb2O3: 0-2 mol %
SiO2+Al2O3+MgO+TiO2: 92 mol % or more; and the crystallization degree of the crystallized glass is in a range of 20 to 70 vol %.
With the above substrates 1-3, the crystallized glass may comprise Y2O3 in an amount of 0.3 to 8 mol %.
With the above substrates 1-3, the crystallized glass may comprise ZrO2 in an amount of 1 to 10 mol %.
With the above substrates 1-3, the crystallized glass may comprise ZrO2 in an amount of 1 to 5 mol %.
With the above substrate 1, the crystallized glass may comprise R2O in an amount of 1 to 5 mol %, wherein R is at least one selected from the group of Li, Na and K.
The R2O is preferably K2O.
With the above substrates 1-3, the crystallized glass may comprise TiO2 in an amount of 8 to 14 mol %.
With the above substrates 1-3, the substrate may exhibit a Young modulus equal to or more than 140 Gpa.
With the above substrate 1, the crystallized glass may comprise
SiO2: 35-43 mol %,
Al2O3: 9-20 mol %,
MgO: 30-39 mol %,
Y2O3: 1-3 mol %,
TiO2: 8.5-15 mol %, and
ZrO2: 1-5 mol %.
With this substrate, a molar ratio of Al2O3 to MgO (Al2O3/MgO) may be equal to or more than 1.35, and the substrate may exhibit a Young modulus equal to or more than 160 GPa.
With the above substrates 1-3, the mean particle size of the crystal particles contained in the crystallized glass may be equal to or less than 100 nm.
With the above substrates 1-3, the mean particle size of the crystal particles contained in the crystallized glass is equal to or less than 70 nm.
With the above substrates 1-3, the substrate may have a polished surface with a surface roughness Ra (JIS B0601) equal to or less than 1 nm.
The present invention further relates to a substrate for information recording medium (hereinafter referred to substrate 4) composed of crystallized glass comprising enstatite and/or its solid solution as main crystals and the substrate has a polished surface with a surface roughness Ra (JIS B0601) equal to or less than 1 nm.
With this substrate 4, the substrate may have a polished surface with a surface roughness Ra (JIS B0601) equal to or less than 0.5 nm.
With the above substrates 1-4, light transparency at 600 nm through the substrate with 1 mm thickness may be equal to or more than 10%.
With the above substrates 1-4, thermal extension coefficient of the crystallized glass may in the range of from 65xc3x9710xe2x88x927 to 85xc3x9710xe2x88x927/xc2x0 C.
The present invention further relates to a substrate for information recording medium (hereinafter referred to substrate 5) composed of crystallized glass comprising enstatite and/or its solid solution as main crystals and the mean particle size of the crystal particles contained in the crystallized glass as main crystals is equal to or less than 100 nm.
With this substrate 5, the mean particle size of the crystal particles contained in the crystallized glass as main crystals ay be equal to or less than 70 nm.
The present invention further relates to a substrate for information recording medium (hereinafter referred to substrate 6) composed of crystallized glass comprising enstatite and/or its solid solution as main crystals and light transparency at 600 nm through the substrate with 1 mm thickness is equal to or more than 10%.
With the above substrates 1-6, the crystallization degree of the crystallized glass is equal to or more than 50 vol %.
With the above substrates 1-6, the total content of enstatite and/or its solid solution may range from 70 to 90 vol %, the content of titanate may range from 10 to 30 vol %, and the sum of enstatite and/or its solid solution and titanate may be equal to or more than 90 vol %.
The present invention relates to a substrate for information recording medium (hereinafter referred to substrate 7) composed of crystallized glass comprising enstatite and/or its solid solution as main crystals and thermal extension coefficient of the crystallized glass is in the range of from 65xc3x9710xe2x88x927 to 85xc3x9710xe2x88x927/xc2x0 C.
With this substrate 7, the thermal extension coefficient of the crystallized glass is in the range of from 73xc3x9710xe2x88x927 to 83xc3x9710xe2x88x927/xc2x0 C.
With the above substrates 1-7, the crystallized glass substantially does not comprise quarts solid solution as the main crystals.
With the above substrates 1-7, the crystallized glass substantially does not comprise spinel as a crystalline phase.
With the above substrates 1-7, the crystallized glass substantially may not comprise ZnO.
With the above substrates 1-7, the information recording medium may be a magnetic disk.
The present invention relates to an information recording medium comprising a recording layer on the above-mentioned substrate of the present invention.
With the above information recording medium, the recording layer may be a magnetic recording layer.
The present invention relates to a process for preparation of a substrate for an information recording medium composed of crystallized glass (hereinafter referred to process 1) comprising
SiO2: 35-65 mol %
Al2O3: 5-25 mol %
MgO: 10-40 mol % and
TiO2: 5-15 mol %,
wherein the sum of the above components is equal to or more than 92mol %, and main crystals contained in the crystallized glass are enstatite and/or its solid solution;
wherein the above process comprises steps of:
melting glass starting materials at 1400 to 1650xc2x0 C. to prepare a glass,
molding the resulting glass into a plate-shaped glass, and
subjecting the plate-shaped glass to crystallization.
With the above process 1, the glass starting materials may comprise K2O and the melting temperature is from 1450 to 1600xc2x0 C., preferably from 1450 to 1550xc2x0 C.
With the above process 1, the glass starting materials may comprise Y2O3 and the molding of the glass into a plate shape is conducted with a mold at a temperature of from 600 to 680xc2x0 C.
The present invention relates to a process for preparation of a substrate for an information recording medium composed of crystallized glass (hereinafter referred to process 2) comprising
SiO2: 35-65 mol %
Al2O3: 5-25 mol %
MgO: 10-40 mol % and
TiO2: 5-15 mol %,
Y2O3: 0-10 mol %
ZrO2: 0-10 mol %
R2O: 0-5 mol % (wherein R is at least one selected from the group of Li, Na and K)
RO: 0-5 mol % (wherein R is at least one selected from the group of Ca, Sr and Ba)
As2O3+Sb2O3: 0-2 mol %
SiO2+Al2O3+MgO+TiO2: 92 mol % or more; and main crystals contained in the crystallized glass are enstatite and/or its solid solution;
wherein the above process comprises steps of:
melting glass starting materials at 1400 to 1650xc2x0 C. to prepare a glass,
molding the resulting glass into a plate-shaped glass, and
subjecting the plate-shaped glass to crystallization.
With the above processes 1-2, the crystallization may be carried out by heating the molded glass to a temperature of from 850 to 1150xc2x0 C.
With the above processes 1-2, the heating may be carried out by heating the molded glass to a temperature of from 500 to 850xc2x0 C. at a heating rate of 5 to 50xc2x0 C./min and then heating the molded glass at a heating rate of 0.1 to 10xc2x0 C./min.
The present invention further relates to a substrate for an information recording medium composed of crystallized glass (hereinafter referred to substrate 8) comprising
SiO2: 35-65 mol %
Al2O3: 5-25 mol %
MgO: 10-40 mol % and
TiO2: 5-15 mol %,
wherein the sum of the above components is equal to or more than 92 mol %, main crystals contained in the crystallized glass are enstatite and/or its solid solution, and the crystal glass does not comprise ZnO;
wherein the above crystallized glass is prepared by a process comprising a step of heat-treatment of a glass comprising SiO2, Al2O3, MgO and TiO2 at a temperature of from 850 to 1150xc2x0 C. to obtain a crystallized glass.
The present invention further relates to a substrate for an information recording medium (hereinafter referred to substrate 9) composed of crystallized glass substantially consisting of
SiO2: 35-65 mol %
Al2O3: 5-25 mol %
MgO: 10-40 mol % and
TiO2: 5-15 mol %,
Y2O3: 0-10 mol %
ZrO2: 0-10 mol %
R2O: 0-5 mol % (wherein R is at least one selected from the group of Li, Na and K)
RO: 0-5 mol % (wherein R is at least one selected from the group of Ca, Sr and Ba)
As2O3+Sb2O3: 0-2 mol %
SiO2+Al2O3+MgO+TiO2: 92 mol % or more;
wherein the above crystallized glass is prepared by a process comprising a step of heat-treatment of a glass comprising SiO2, Al2O3, MgO and TiO2 at a temperature of from 850 to 1150xc2x0 C. to obtain a crystallized glass.
With the above substrates 8-9, the heat treatment may be carried out for 1 to 4 hours.
With the above substrates 8-9, the heat-treatment may be carried out at a temperature of from 875 to 1000xc2x0 C.